The present invention relates to novel concepts for gas treatment and gas cleaning, in particular for cleanroom conditions.
More particularly, the present invention relates to a filter material useful in particular in filters or as a filter for gas treatment and/or gas cleaning, in particular for cleanroom conditions, and also to methods of producing said filter material and also of using said filter material.
The present invention finally relates to a method of cleaning/conditioning gases by using the filter material of the present invention.
A cleanroom in the context of the present invention is a very clean room in which the concentration of airborne corpuscles and noxiant gases is kept as low as necessary. Such cleanrooms or very clean rooms are needed for special methods of fabrication particularly in semiconductor fabrication/technology—where particles and gases found in ordinary ambient air would disrupt the particular methods. In semiconductor fabrication in particular, particles just a few nanometers in size can disrupt the structuring of integrated circuits; it is similarly possible for disruptive/oxidizing gases, e.g., oxides of sulfur and of nitrogen, hydrogen sulfide, ammonium, halogens, hydrogen halides, etc., which are ever present in the atmosphere, to disrupt/impair such fabrication processes (e.g., misdoping of semiconductors, etc.).
Further applications of cleanrooms and/or cleanroom technology are found in optics and laser technology, aerospace technology, the biosciences and medical research and treatment, the research and germ-free manufacture of foods and medicaments and in nanotechnology.
Cleanrooms of this type are generally designed such that the number of airborne corpuscles introduced into or possibly formed in the room can be kept as low as possible. Various filtering devices equipped with particle filters appropriate to the particle size are used for this purpose. Depending on the field of application, the requirements as to the maximum number of corpuscles/particles in the cleanroom or very clean room can vary. There may be an additional provision to control, for example, not just the particle count but also the number of germs, which is needed in the manufacture of pharmaceutical products or products of the food industry in particular. Other parameters, such as temperature, humidity and pressure, are generally likewise kept constant to create comparable conditions at all times.
A central aspect for the provision of cleanrooms is represented by the flow principles of the room air to be filtered to minimize corpuscles and/or germs and/or noxiant gases. In general, cleanroom technologists distinguish between a turbulent diluting flow and low-turbulence displacing flow. In the turbulent diluting or mixing flow, the filtered clean air is introduced into the cleanroom in turbulent fashion and thereby produces a monotonous dilution of the particle/noxiant gas concentration. However, it must be borne in mind here in particular that objects and processes which generate particles and noxiant gas are eliminated in the cleanroom. In the low-turbulence displacing flow, which is also known as laminar flow, the clean air flows into the cleanroom in a low-turbulence manner and generally vertically and has the effect that the vulnerable workspaces and machines are contaminated as little as possible. The air then escapes from the room on the opposite side, generally through a perforate double floor and is returned to the air circulator for repeated filtering.
Owing to the different levels of cleanroom requirements, the various fields of application have their own cleanroom classes and standards regulating their adherence, in particular for cleanrooms used in microelectronics. For instance, semiconductor technology is governed by ISO standard 14644-1, which provides classes from ISO 1 to ISO 9, where ISO 1 is the class having the highest requirements with regard to cleanness.
Various methods are employed to meet the particular requirements of the particular field of application and to prevent unwanted particles and noxiant gases and/or the particular main contaminants being able to pass into the air and to remove particles and noxiant gases already present in the air.
Numerous filters and/or filter materials are known from the prior art as being potentially useful for the filtration of air from cleanrooms.
Filters and/or filter materials used in particular in the prior art, in particular for reducing the concentration of noxiant gases, are based on activated carbon and are generally endowed with suitable impregnants for the activated carbon, since the sorptive properties of the activated carbon may otherwise often be insufficient.
One disadvantage of the customarily used activated carbon filter materials, however, is that even with suitable impregnation the adsorptive performance is insufficient at very low levels of noxiants/gases to be removed, since adsorption often only ensues beyond a certain threshold value. As a result, low levels of undesirable noxiants and gases can in this way “slip” through the filter materials and cause undesirable contamination of the cleanroom atmosphere.
Sulfur- and nitrogen-containing gas and noxiant materials, such as oxides of sulfur and of nitrogen, ammonia, hydrogen sulfide, etc., are removed using specifically iodide-impregnated adsorbents, in particular iodide-impregnated activated carbons, by the iodide impregnation reacting with the gas and noxiant materials to be removed and in the course of this reaction being partly converted into elemental iodine which, after a certain in-service period of the filters and/or filter materials, can escape/desorb from the activated carbon, so the cleanroom atmosphere becomes undesirably contaminated with iodine.
WO 01/70391 A1, for instance, proposes the use of a filter material having adsorbing properties which includes a carrier layer as well as a plurality of adsorbing layers. It is provided therein that the filter material shall include not only at least one adsorbing layer based on an impregnated activated carbon material but also at least one adsorbing layer based on ion exchange materials. The impregnation contemplated for the activated carbon material is in particular an impregnation with metals from the group of copper, iron, nickel, zinc, chromium, cobalt, ruthenium or osmium. The impregnation of and for the activated carbon material is relatively cost-intensive. Impregnation is further not always efficient in that, more particularly, some of the noxiants can be freed again by desorption processes. Moreover, slippage at low noxiant/gas concentration is relatively high.
DE 196 30 625 A1 further proposes a method of extracting impurities from a gas. It is provided therein that a gas stream containing water vapor is passed through solid sodium iodide to trap/bind the contaminants through formation of sodium iodide hydrate. The sodium iodide can be in the form of finely granular sodium iodide powder, in the form of a coating on a carrier material or in the form of a porous solid sintered body. However, the sorption or reaction of acidic or oxidizing gases, especially sulfur- or nitrogen-containing oxides, hydrogen sulfide or the like, can cause significant amounts of elemental iodine to be formed and released into the atmosphere in the course of operation, leading to an undesirable contamination of the ambient atmosphere. Moreover, the initial adsorptive performance is unsatisfactory, in particular at low levels of noxiants/gases to be adsorbed.